1. Field of the Invention
The present invention relates generally to digital circuitry, and more particularly, to the management of power consumption of digital circuitry.
2. Related Art
In many electronic applications, and in particular in the medical device field, power consumption is an important consideration in product design. With respect to implantable medical devices, power consumption can be a critical issue. The power for an implanted device can be supplied from an external device through the skin using a wireless link or percutaneous lead, or, alternatively it can be supplied via an implantable battery. In each case, the available power within the implant is limited. As such, to provide the implant with a sufficiently useful operating lifetime, the limitations on the power supply push demands to lower the power consumption of the device.
One way to reduce the power consumption is to reduce the supply voltage of digital circuitry such as is found on an integrated circuit (IC). However, reducing the supply voltage produces consequential drawbacks. When reducing the supply voltage, the delay of the digital cells increases and as a result the timing of the circuitry becomes a critical consideration. As such, for digital circuitry, there may be a lowest threshold supply voltage level which provides optimum power consumption. However, going below such a threshold would result in the circuit not meeting the timing which is necessary for the designed function of the circuit. Such an optimal point would be dependent on the IC processing, the specific IC parameters, temperature, aging of the device, the patient's settings and operating demands. Hence, the supply voltage level which provides the optimal power consumption can differ from chip to chip. Further, the optimum supply voltage level for the one circuit will change dynamically as operating demands will change depending upon a patient's requirements.
An example of a conventional implantable hearing system is illustrated in FIG. 1. The system consists of an external part 12 and an internal part 14 (i.e. the so-called implant). External and internal parts 12, 14 communicate with each other using a wireless link 16 through the skin. Both internal and external parts 12, 14 can consist of one or multiple components. For example, an external sound processor 18, for capturing the microphone signal and conditioning the signal before sending it to the implant 20. Other external components could be a remote control 22, a programming interface, a diagnostics device, additional microphones, etc. The internal part 20 typically has a stimulator component that is responsible for stimulating the auditory nerve. Internal components may also include an implantable battery, implantable microphone, a receiver for a wireless link, etc.
As shown, each component can include a number of ICs which provide different required functions. In the illustrated example, the sound processor 18, as well as the implant 20, each includes a digital IC 24, 26. Such an IC can contain some analog blocks, but the majority of the IC consists of digital logic and memories.